Availability of network connections has been the focus of increasing interest in the telecommunications field. In particular, the practice of maintaining redundant network devices and connections has become commonplace. Under the practice of redundancy, when a failure is detected in a network device or connection, network traffic is switched to a standby network device or connection. While some data may be lost in the switch-over process, most network protocols, for example TCP/IP, have integral recovery mechanisms, such as retransmission of dropped packets, that are intended to minimize disruption of network traffic during a switch-over from active to standby equipment or connections. If the disruption is brief, these recovery mechanisms will maintain network connections. However, if the disruption is more prolonged, connections may drop.
The multiprotocol label switching-transport profile (MPLS-TP) framework requires support of the transport entity or trail recovery. For example, in the event of a span or a node failure of a label switch path (LSP), pseudowire (PW) or sub network connection (SNC), the entity should recover within 50 ms of the failure. This is known as a sub-50 ms recovery, or a sub-50 ms traffic hit. References to a transport entity in this document are applicable to LSP, PW and SNC.
Several MPLS-TP mechanisms exist to accomplish a sub-50 ms node or span failure recovery by defining a second transport entity, the protection entity, between the same endpoints as the original entity, the working entity, where the working and protection entities do not share the span or nodes against whose failure protection is required. When a failure is detected at the working entity, the endpoints switch traffic to the protection entity. Traffic recovery is expected to occur within 50 ms of fault detection. These mechanisms rely on proactive connectivity verification between the endpoints for fast failure detection, and support both 1:1 and 1+1 protection architectures.
Examples of such mechanisms can be found in IETF draft-ietf-mpls-tp-linear-protection, IETF draft-zulr-mpls-tp-linear-protection-switching, and ITU-T G.8131 T-MPLS Linear Protection. However, in network environments where span or node failure likelihood is relatively high, existing MPLS-TP linear protection mechanisms may not meet operator availability requirements since they may not protect against one or several failures affecting both the working entity and the protection entity. To overcome the abovementioned shortcomings and meet operator requirement in such an environment, there is a need for a protection mechanism to provide sub-50 ms recovery in the event of a failure in any of the transport entities.